In mammalian heart, a comprehensive array of voltage-gated potassium (Kv) channels serve to drive myocyte repolarization by opening in response to depolarization to allow K+ ions to leave the myocyte and restore a negative resting potential. Disturbances in the efficiency of this process lead to delayed myocyte repolarization, and can cause long QT syndrome in human patients - if not corrected this degenerates into torsades de pointes and ventricular fibrillation, associated with syncope and sudden death. Repolarizing force is governed by the sum properties of the functional channels in the myocyte plasma membrane at a given time, i.e. those particular channels that have been assembled, trafficked to the membrane, and not yet recycled for degradation. Little is known about the factors that govern these all-important elements of cardiac Kv channel physiology. Preliminary data show that single transmembrane domain, Kv channel ancillary subunits called MiRPs (MinK-Related Peptides) can act not just as biophysical modulators of Kv channels, but also as molecular chaperones that determine Kv channel subunit composition and fate. Inherited mutation of the KCNE genes that encode MiRPs is associated with both inherited long QT syndrome, and with increased susceptibility to drug-induced arrhythmia, an equally malignant and far more common disease. Thus, we argue that a full understanding of the impact of MiRPs on Kv channel physiology will aid our understanding of cardiac disease and potentially lead to targets for rational drug design. Here, we apply a combination of electrophysiology, molecular biology, protein chemistry and confocal microscopy to explore two novel paradigms for MiRPs and for Kv channel pore-forming subunits: (1) The ability of MiRPs to coordinate internalization of Kv channel complexes from the plasma membrane will be explored, and the MiRP sequence motifs that govern this process identified. (2) A novel role for MiRPs will be examined, as molecular matchmakers that favor incorporation of some A-type alpha subunits into heteromeric channel complexes, thus governing Kv channel composition. (3) Preliminary data suggest several novel cardiac Kv channel complexes: their presence will be determined in canine and rat heart using classical biochemical techniques. Knowledge of the diverse functions that MiRPs subserve in Kv channel complexes will aid in efforts to understand, treat and avoid inherited and acquired disorders of cardiac electrical function. [unreadable] [unreadable]